I need a compound that is harmeless to the human body, odorless, tasteless, causes some kind of visible reaction (urine coloration perhaps) AND can be bought without medical recomendation.
Food stealing in my company fridge has become a serious problem. It's not only a recurring issue but a targeted one... our thief has been targeting "high" value, particularly coconut water. HR seems to ignore our complains... so I decided to take matters in my own hands... since I have access to timesheets, I thought that if I can scare out thief to leave work or skip it, I can narrow-it-down/point-him-out because we have about 30 people in our office...
Urine typically is yellow, but in combination with blue dyes, a green colour can be obtained.
Noteworthy compounds are methylene blue, thymol, Cimetidine (antacid), or Mitoxanthrone (used in cancer therapy).
I've mentioned these just for the sake of completeness - I think it is irresponsible and stupid to spike food with anything that doesn't belong there.
Hiding a webcam in a shelf and running zoneminder probably isn't legal either and will get you in trouble with the privacy officer, but at least that doesn't mess around with the health of anybody else.